Distortion neutralizing repeater



Dec. l, 1931. H N YQUlsT 1,834,002

DISTORTION NEUTRALIZING REPEATER F'iled Sept. 17, 1929 2 Sheets-Sheet l V" M l 1 Dec. 1, 1931. H. NYQulsT r 1,834,002

DISTORTION NEUTRALIZING REPEATER Filed Sept. 17. 1929 2 Sheets-Sheet 2k 21u each.

INVENTOR WQ A ORNEY 1 An arrangement, such as Patented Dec. 1, 1931 UNITED STA-' HARRY NYQUIs'r, or MILLBURN, NEW JERSEY, As'sIGNoR fro AMERICAN TELEPHN' f AND TELEGRArH COMPANY,` A coRroRATIoN or1%r1a.W,YonK;y

Drs'roRTroN NEuiraALIzInG "REPEATER applicati@ sied i september 17, y 1929. serial nu.' k:sas-,1242.4

This invention'relates to-wave translation systems, as for example, systems for amplify-V ing electrical variations 'with the aid of electrical space charge devices, and more particu-A m output wave from the'output of an amplifier which distorts, neutralizing the undistorted portion of the wave-thus pickedoff by means of an undistorted wave from the input of the' amplifier, and then impressing the resultant l; wave which comprises distortion components only upon the input of the kamplifier in such phase and amplitude as to neutralize the distortion due to the amplifier. Such a system,

if it could be perfectly adjusted, would not :ai only be substantially distortionless but would also compensate for variations in thel gain of the amplifier due to variations of its circuit constants and would thus tendV to maintain the gain uniform. i 1

described, involves a repeater with a feed-back circuit of a special type and inherently the perfection of its operation` depends upon the :bala-nce. Since it is impossible, in practice, to obtain a :n perfect degree of balance, it may happen that a repeater provided with a special feed-back arrangement of the type above described `Will not meet the requirements ,whereja veryhigh degree of freedom from distortionis nece'si3 sary. Accordingly, 1t 1s proposed, 1n accord`- ance with the present inventiointo provide in a repeaterof thetype above vdescribed an amplifier of vsuch character-that the inherent distortion which must b'eibalanced out will be il reduced to the smallest possible limits. To

.accomplish this result, itis Vproposed to substitute for the ordinary multi-stage amplifier in such a repeater circuit a repeater that in itself is provided with a feed-,back connec- 'f tion. The result is that the repeater includes a distortion neutralizing feed-back circuit within another distortion reducing feed-back circuit. c, Y

The invention will now be'more fully "0 understood-from thek followingdescription *heamplifying units "C and E lbeing worked when read in conneotionwith the drawings-1in which Fig. 1 is a Schematic diagram, of a typeof repeater to whichthe inventionmay bey applied;l Fig. 2 isv a schematic diagram showing howy the ordinary amplifier of a.,di`s l tortionneutralizing feed-back arrangement` may' be replacedby an amplifierV which, in itself, is provided with a distortion reducing feed-back v( :i'rcuitgFigs 3 landtv are symbolic diagrams illustrating modifications ofdistortion reducing amplifiers which maybe utilized in the -circuit of Fig. y2 andFigs 3 i (a) and 4 (a) are diagrams showing inmore de'- tail circuit arrangements for carrying out the invention as embodied inFigs. 3 and 4, respectively.

` A distortion neutralizing repeater ofthe type Ito which the present invention vis to'be applied is illustrated in Fig. 1 and comprises 'amplifier elementsC, D-and E connectedby,

means of kcircuits M, Ny and S, as shown.- In this type of repeater, the amplifying unit D -is the principal amplifying unit-forbringing thecurrents up t'o the desired large' volume,

lat 'suchlow levelsthat the'non-lin'earirdis-l tortion `dueto their action may be neglected.

Due to the high levels at whichamplifier D mustbe worked, such amplifier,'if theiordinary `multi-stage vacuumtubeitype, will? have a certain amount 1 of f non-linear i, distortion and S to compensate.y i Y 1- n i, c. A. i

Let yus assume that a pure sinusoidal wave is applied to tlie'repeaterof Fig. 1A and' that the `amplifier- E is not. functioning. A; V pure sinusoidal waveiwill then appear at the point A'between amplifiers vC and D. On. the-out? putsidevof the amplifier D, a Vsimilarjsinu-c; soidal wave appearsV but it'hassuperposed thereony certain 7'distortion currents, ,By means ofthe resistance coupling X1, X2 and lX3, the `circuit M `picksgoff aportion of the of these two waves areproperly. related,f theL f which itis rthe function of the amplifiers C and-E 4with vtheir associated circuits .M, ,N

sinusoidal. wave coming over .the circuit Ny l from the point between amplifiers C and D Vwill just neutralize the sinusoidal part of the Wave coming from the output of the amplifier D. VvAs a result, the'reurrent which is applied t' ithe' input-ofthe .amplifier D Crand D and will appear iin \the .output. lf

' care is taken to properly relate the ampli- .tude and phase of .this v.-distortionl Current;

(which was applied to the'y circuit over the #partirV to the ,-phase an d the amplitude l of Vthe' 4distortion Components o'f ythe sinusoidal Waveafter transmission through thev ampli- 'fier TD, tl1-'i s distortion -iuayfgbe -made' ftof -neutralizethe distortion generated in thev arnliffiger' ED `so 4th a'tfthe lultimate output -ofv the i lamplifier D fwill lleve an iundistortecllsinusoidal the amplifier `^E iis vmadev somewhat l.too great l"(or' too-smfalfl)',the repeater will be made to :over-correct for' under-correct) "the distertion :so thaft -distor5iongenerated infthe amplitier fC may ibe lleempensated, assuming,

` 'however, lthat fthe amplifier LC has fthe same 1 'son fini-battery 'veluesproportion of second and third harmonies 'as the arnplifierD.

' V A repeater-sudhlas aboveldescri'bed haslan- .other desirable property in ythat .it tends tov veoinpensate for `variations '-in gain.v 'For eX- 'am'ple, `-suppose the kgain iin amplitier D ehangesydr some reason, such as -a varia- As a result, :the

. undamentallwave not Completely neutralized before-entering amplifier E'. YInother eenling"v from the circuit N,the plraiseof theV "55,

words, aportion of .theffundamental Wave lis-aanplfilied vby 4'tl-1efaaliipilpifier Etas Weill ,as the distortion; l1: .The net result offthisfunda-- "mental waive component whenl applied to .the

ainplifier') 'is to `keep the outputjin 'the line const/ant,V For' exam-pleg, :if the fundamental Y eoming' f from the circuit A1M is greaterfgthan'fthat 'coming from` the cireluit N, the riis`ul'tan-twave passing :througlrthe i y amplifier E will be in suehphaseas to oppose the Vegreesstrarrsmittedfrom ftliekoi-itput .ofithe yanilplifier1l) to the firc'ulit OnA theV other A'ing-1 from the-circuit VM is smaller than that resultant Wave passing t'lirougji the amplifier E, will beisueh as toV add tothe 'fundamental f component appearingin lthe output circuit of @beweren gna.:

the,amplifierD.V In other words, the circuit -not"onl 7 tendsto keep-*the distortion zeno but tends-to leepvariations in the, gain of the amplifieriDfrogn having any effect on .In y orderftoi get proper yfunctioning with .this Vtjqie of apparatus, it 'is neeessa'rytliat the phase relatinsbetween the'va'rious wave be approximately right. YThis leads to the following requirements: (l) The amplifiers C, D and E must be resistance Coupled or very nearly so. (2) The total number of the stages in ampliiier D must be an odd number. Y Thejtotal number of 'the stages in amplifier `E 5plus amplifieriC must be f an even number.

Any .numberof .stages may .be .used .in .the amplifiers kC, "D E, siibj elet `to` the Wforegoing requirements, dependingupon the desired-frain.;bviously, stages may be taken from the amplifier D and added to C so long 'as the number-1in ADremains odd and the sum of the stages inC and Ef is even. There is a Vdistinetdisadvafntage'inthisfhoweveig in that 'the-stages lin the, amplifier C will'-not-bewith Ain the compensated 'portion Yof the circuit. vrTherefore, any distortion generated in these stages Vwould flee imperffeo'tly compensated EFurtherinoi-'e,` variations in ithe gain of the amplifier C would lnot be properly compensated. @n the-other hand,'the stages-ofthe amplifier C- may Jallflo'ev embodied 'in the `am- :plifier provided fthei'lnumber ofv stages is even.y On the whole,fthe .preferred desi-gn would {a'pear t'o lbe a l'-l-imitegl 'even :number -o-f stages infarnplifier and `the necessary Vodd number of stages'in'anrplifier D, withithe amplifier fC eliminated entirely so that 'the paths S-a-n'd '1N w-illbebridged together across Ythe input -eireu'itofithe amplifier D. VtIn Fig. l-oi jthe drawings, 'a speei'fiedesigni's indicated ini-which five-stages are lemployed in amplifier D and two stages in amplifier E with `nostages in ampli-fier C, these conditions being indicated by thenufnierals below the dette-rs indicating the amplifiers.

inthe foregoing discussion of the :operation, fitfi-s assumed conditions are ideal and where leert-ain components are to be neutralized orbalaneed out, the conditions of balance will perfect: In actu'allpractiee, however,

these -Condit-ions do not obtain and some distortion will appear'in the output 4of the repeater 4eiven with rthe neutralizing :feed-back combination MNSE provided. For example,

theV ainplifierD (may looked upon as inl'ierently vintrodu'eirig a fcertain amount of non-lineardistortionwhich is, say, N deeibefls f below" the main transmission. The eed-bac'lrgapparatus "shown in the igure may 'be thought-oies reducing this distortion by an amount, say, ltl decibels. rJ'Che total ef- `feet' is that the resultant distortion is 'down by'N-l-N decibels from fthe main transmission.- Now, suppose,fwe'li`ave an operating VconditionA which requires that N-l-l should equal 75. l"Under the best eonditions'of balance., the feed-back arrangement might be in- 1 .capable of making a reduction fin distortion l suehfthat N 'would be larger than 35. inl order. to meet the required condition, it would be necessary for the amplifier D to be suffiiently distortionless .so that the value of Y kdistortion neutralizing repeater involving f Y where the amplifiers F', C and E are of one N would not be lessthan 4Q, ay conditionwhich is difficult of attainmenti by the use of ordinary amplifiers. p 1 A.

In order yto overcome this dificulty,fit is proposed, in accordance with `the present invention, to reduce the distortion introduced by the amplifier D of Fig. l bypmaking the amplifier D in the form of arepeater with af` being a straightforward*multi-stage amplifier will now in itself assume the form 'offa the main amplifier D, auxiliary amplifiers C1 and E with associated feed-back connectionsM, N and S. These elements all tend to function in the manner already described, with the result Lthat the apparatus comprehended within the dotted rectangle D will in itself tend toreduce the normal distortion due to they operation of the amplifier D', this distortion being further reduced by the normal feed-back arrangementcomprising circuits M, N and S together withauxiliary amplifiers C and E.

If, however, the circuit'ofFig. .l2-is .con-.-

sidered more' critically, it becomesr evident that there exists a difference between the type of amplifier shown within the dotted lines D and the ordinary one-way multi-stage amplifier. Whereas an ordinary one-Way amplifier does not transmit any wave backward from its output to its input, the arrangement within the dotted lines D does return such a wave-as a result of current delivered by amplifier-IE.

lVith a circuit arrangement such asL shown in Fig. 2, some of this current would find its way into the amplifier E over the path and thus upset the neutralization which-would normally be expected to result fromtheuse of the feed-back circuit M. rv.In order to preventv such false action Yof the circuit shown in Fig. 2, it is necessary torprevent transmission in the reverse direction at the pointsv This may be accomplished by introducing a one-way device such as an amplifier at the points m-y so that transmission cannot take n place from S to circuit N. With the' introduction of such a one-way device, the apparatus comprised withinthe rectangle D may ytake the form indicated in Fig. 3where a one-way device F 1s connected ahead-of the number, of stages in these threev amplifiers being an vodd number, therefore conforming to the requirement for amplifier D, as previously. laid down. cThe numberof stages in the amplifierD must also be anodd number forV thesame reason as'given 4for,v theamplifier D, which means that the total number ofstages in F and Cmustbe an even number,

In accordance with requirement (3) `previously laid down for the arrangement of'Fig. l, it followsthat the total number of stages in ampliers C andrEv must be an even number. These various requireymentssare satisfied by thecdesigninjFig. 3

(in .whichthe number'of stages vin eachV an'iplifier is Vindicatedfbyvv the .numer'albe- Y low the letter;t designating the amplifier) stage each and amplifier VD comprises three stages. The resultant-amplifier, corresponding tothe amplifier-D of Fig. l, requires, in effect, only 4one `additionalamplifier tube,

namely,.that of the one stageA amplifier F4.

. A slightly different design for the/amplifying Vapparatus kwithin the rectangleD `is illustrated in vFig'. 4.; Here the foregoing .design requirements are'satisfied by making vamplifiers F and C of two stages each; arnplifier D of one stagegfwhile no stages are comprised lwithin the arnplifierFi. It will l bel seen that'th'eftota'l stages in F', C. and D is'an odd number." `D itself comprises an odd number and-the totalnumber of stages in amplifier E andjC vcomprises an yeven number. This arrangement has thev advany, tagethat it provides a substitute for the amrplifier D of Figi, which utilizes only five stages of amplication and still provides a neutralizing feed-back. -arrangement forreducing 1 the distortion. However, it. has `the c disadvantage, vas comparedto Fig. 3, that only thev distortion due to the one'stage am- .c plifier D. is f compensated.- While.' vit -is Y true' that by` Vmeans .of over-compensation for under-compensation itfis possibleto ltake care y ofthe other stages .(F and C( in part, nevertheless, Jthisarr'a`nf .;enient, .in this respect, wouldlbe somewhat inferiorqtogthat of Fig. 3.15It isone which might'be preferred to it, however, where greater simplicity .is de-V.

`sired than inthe case' of Fig.3.- f

Variouslother combinations of stages are possible but the arrangements shown in'Figs. 3 and 4 are sufficiently illustrative of the ,principle so that itis deemedunnecessary to illustrate, .other modifications whichwill obviouslysuggest themselves. f

of the 'one-stage amplifier C is yalsogcon- 'I The schematic arrangement shown-in Fig. ..3 is, illustrated in-more detail in Fig. 3 (a). As will be seen, theoutput of the three-stage` amplifierD is connected by means of a feed- `back circuit M" to the input of the auxiliary one-stage amplifier i.

The Youtput n iiiifplnion performing Itho iiiiiotioii, of 'amiplifioilnfo'iflfig. 1. Tlio loutputgoi this itin-- vpliiioi arrangement is ooimoo'tod bymoans A of? the N tube i's'about onevolt While that of tno-.L tulo-ois about 4 lvolts. Foi-fpioporopoi 'a on grid 'of the ANtu-be should be biased jljtil'ltfi Volts more "negative than its filament tylitille'tlie -Iftlbe sll'illd have v its-grid potential about 9 volts `l`iegatiye -with respect to the filament. The "cificfilit iss arranged that the ilanieiits fof yall ofthe 'tubes are onnected in "ser'esfas w'ill clear from an inspection vof p u r'om'taps 'in the ii-lanlentisupplycircllit.V In -30 ordei1 tol accomplish this result, :a number of liosisto'ooos, about twofoli'oos ottoii oro Ipiofilefd tle i-lanellt rSlipply circuit SO that Ethc'l, dropfifsfabo'utequiyaent to that "through tubes it'o faire fcaie ofthe fa ct 'that vtllkftil ament torrent for fon N tubo is only' 1r! ampere as Vcoifnpaied With t1/2 aln'lere for tlleQL tube. If the 'cnnec'tionsffion tlifeg'rid t'o the'va'rious tubes v'inthe 'filial-nent supply 'circuit be traced, it vwill be Yfoundftliat tl'le gr'id of 'each ,N tube AWill be connected 4to a point/in the filament ""supplygcircuit biased '6 *Volt-s more negatiX/"e tlian'tlie negativo sido 'of itsv filament while tleL tubeW/illhave its grid Econnected*to a point about 'evolt-s negativo with iospo'ot to its 'filamenti ni analyzing ,tliosoooooootioiis it A"tubos 'oro toniiootod tlio following 'foi'tlo'fz l C", y'tilbe Ni of amplifier E", tubes N5 and N6 1 'of ampliiiei Efand -nally the tube N7 of the VanoplifieiF.` 2' i Y Thiefscheniatic' "arrangement of Fig. 4 is lalsfo showin in more detaii i'n` F ig. 4 Here the amplifier D( comprises a single L tube designated Lv; The 'ampliierE is eliminated and the lamplifier IG comprisestwo N'tubes.

V `liso The -one-'vvay device F also comprises two u tutos' as doo-S' tho tiiiliiiy amplifier n oi the iria-in oiit'uit;

arrangement slov'vls that it koofnfo'rms to the n schematic layout of Fig. 4 and Will therefore esooperate in theliiiannor previously described.

Ana-lysis of this f circuitV 'rloiaagoia thoV filomoiits'of' r4all of tho tubos "arec'onnected in seriesintlie same filament supply circuit and the potentials offtlie-grids are obtained t:trom'taps vint-lie ilan'ient supply Kcircuit for Awhich purpose a number of tfwo- 70 ohm regsifstances are "connected in t"series, -eujh of Whichfwill have adrop about equivalentlto "tliattlirough @the lamentjofone-'Ntubef By tracing tho 'oonnoo'tioiisof jtlio various 'grids to the Various taps in thefilamentsilpply'oirj cuit, 'it .'Will 'beseen that the grid of the; L tube is'v 9 Volts negative Wi-tli respectto 'its filament and the grid-ciottoli N tubeis :biased negativo l 'aboutG- volts. VInftrac'i'ngtilese connections 'it should be' borne 'lin mind ftha't the iilamentsgO of the 'tl'lbes-"arev connected in the following ordern Fr'suthe 'tubo FIJI, thon N tubes Nl and N2 1ofalnplifier C", followed by the tuo i followedvbytlie tubes and N6 of the al'lxiliary lamplifier E. 1 i

A It ywill to' vobvious Vtho-t tlio :gooorol .priociples herein disclosed may' be embodied in many other organizations widelyfdiiferent from those illustrated Without vdepartin{ ,r*1)0 from 'the spirit 'o'i vthe-inv'el'ltion `as Vdefined in 'the-i'ollowing c'laimsp@Y Wh'tis lclainledis: p 1 v l. yIn a distortion neutralizing repeater, a ii'i'ainf amplifying"arrangement including. aiuti princ-ipalnniplilie'r,an auxiliary amplifier2 a `vfeed-back cnn'ection'fro'm Vthe output' of 'saidv -pr'i'ncip'alamplifier rt'o tliefinput of said prin-y cipal a'nlplifienand "aconnection the input 'of said principal -arnplie'r to the inputf 100 of said auxiliary kal'nplilier;a "second 'aux- -iiiary amplier, 'a feed-back Connection from Vthe' output 'side of 'sa-id mainamplifying arrang'einenty through` said' Vsecond `allznliary plifying arrangement", and a Connection from n "tl'e input'side of said main-'amplifying ariangementto the-input of saidseeo'nd auX- j2.Y In `a-'d`istortio'n neutralizing repeater, 'a ',110 imain amplifying'arrangement incll'ldi'n'g a principalamplifier,V an Vzulxiliaify amplifier, a'feed-back connection from the 'outputof said'principal amplifier through saidau'x- 'iliary ampliliert'o the input "of said prin-V115 'cipal amplifier, and'V connection from the input of said principal 'ampliier to the input of said auxiliary amplifier; a Second auX- `iliaryfttn'lplifler, a feed-back connection from I 3; In a distortion neutralizing repeaterg'a 13o main amplifying arrangement including a principal amplifier, an auxiliary amplifier, a feed-back connection from the output of said principal amplifier through said auxiliary. amplifier to the input of said principal. amplifier, and a connection from the input of said principal amplifier to the input of said auxiliary amplifierya second auxiliaryamplifier, a feed-back connection from the output side of said main amplifying arrangement through said second auxiliary amplifier to the input side of said main amplifying arrangement, a connection from'tlie inputv side of said main amplifying arrangement to the input of said second auxiliary amplifier, and a one-Way device interposed ylJetWeen said first-mentioned feed-back connection and said last-mentioned connection to said second auxiliary amplifier, said device being soy poled as to prevent transmission from the former connection to the latter connection. Y.

l. In a distortion neutralizing repeater, a main amplifying arrangement including a principal amplifier, an auxiliary amplifier, a feed-back connection from the output ofsaid principal amplifier through said auxiliary amplifier to the input of said principal amplifier, and a connection fromthe input of said principal amplifier to the input of said auxiliary amplifier; a second auxiliary amplifier, a feed-back connection from the out-y put side of said main amplifyingarrangement through said second auxiliary amplifier to the input side of said mainamplifying arrangement, a connection from the vinput side of said main amplifying arrangement to the input of said second auxiliary amplifier, and a vacuum tube amplifier interposed between said first-mentioned feed-back connection and said last-mentioned connectiony to said second auxiliary amplifier, said vacuum tube amplifier being so poled as to prevent transmission from the former connection to the latter connection.

5. In a distortion neutralizing repeater, a principal amplifier, an input connection thereto, a first auxiliary amplifier, a feedback connection through said first auxiliary amplifier to the input of said principal amplifier, a neutralizing connection from the input of said principal amplifiery to said feed-back connection to produce at least partial neutralization of components of Waves fed back Ycorresponding to the inputl Wave; a second auxiliary amplifier, a secondL feed-back connection from the output side of said principal amplifier through said second auxiliary amplifier t0 the input side of said principal amplifier, and a second neutralizing connection fromthe input kside of said principal amplifier to said second feedback connection to at least partially neutralize components of Waves fed back over said second feed-back and corresponding to Waves applied to the'inputvside of lsaidprincipalaniplifier. l v, y.

V 6. y In" a ldistortion I'ieutrfa'lizingV yrepeater,'` fa vprincipal ,'am'plifier, fan l [input connection .thereto,a Afirst auxiliaryy amplifier, afeed.-

ainplifie'rto the` input of-'lsaidp'rincipal amfeed-back.connectionto producent least parbaek Connection through Sardara aaxiiiaryilm tial neutralization offcompfonentsof v vaves n 'fed hacllcorrespondin'g to' the ,input Wave; `a second auxiliary amplifier, ay secondL Lfeedback connection from the loutput sideof said principal' Vamplifier through `said second auxiliary amplifier to theinput side ofIsaid Y.

principal amplifier, a second neutralizing connection vfrom the input side of said prin- "cipal amplifier yto said secondfeed-back connectionto at least lpartially neutralize componentsv of Waves fed back over said second feed-back and corresponding to Wavesapplied to the input side ofsaid principal amplifier, and means to prevent transfer of energy from said first feed-back connection to said vsecond neutralizing connection. Y

f7.L In a distortion neutralizing repeater, a

principalv amplifier, an input connection thereto, a -first'auxiliary amplier, a feedback Vconnection through said first auxiliary amplifier to the input of said principal amplifier, 'a neutralizing connection from the 'input of said principalsamplifier to saidv feed-back connection to produce at least partial neutralization of components of Wave; 'a second auxiliary amplifier, a second feed-backconnection yfrom the output .Waves fed back corresponding to the input side,rof said principal amplifier through.

said second auxiliary amplifier to the input side. of said principal amplifier, a second'y over said second feed-back and correspond- 'Y ing to waves yapplied to the input side of said principal amplifier, and a one-Way device so connected as to preventtransfer .of

energy from said first feed-back connectionv .to said second neutralizing connection.

8. Ina distortion neutralizing repeater, a

'principal amplifier, an input connection thereto, a first yauxiliary amplifier, a feedhack'y connection through said first auxiliary amplifier to thek input of said principal am-v 'plifier, a neutralizing connection yfrom the input of said principali amplifier `to saidv feed-back lconnection to produce at least partial neutralization ofcomponents of Waves fed back corresponding to the input Wave; la second auxiliary amplifier, a sec'- ond feed-hack connection from the output side of said principal amplifier through i said second auxiliary amplifier to the input 

